JPH0812934B2 - Oxide superconducting device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state electronic device using an oxide-based superconducting (also referred to as superconducting but also referred to as superconducting here) material.

The present invention relates to a lateral junction type Josephson device having an input terminal and an output terminal, an electronic device using the proximity effect, or a four-terminal (including three-terminal) device using a control electrode in such a structure. Regarding

[0003]

2. Description of the Related Art Heretofore, attempts have been made to form a solid-state electronic device by using a superconducting material, for example, a metal material such as Nb-Ge system (for example, Nb ₃ Ge).

A typical example is the Josephson device shown in FIG. This Josephson device is intended to perform switching by combining a superconducting phenomenon and a tunnel current phenomenon, and is composed of a two-terminal circuit. As shown in FIG. 1, this Josephson junction type device has a first superconducting material.
Insulating film (23) with a thickness that allows tunneling current to flow on the upper surface of (21)
Was formed, and the second superconducting material (24) was further laminated thereon. And it relates to a vertical junction type in which a tunnel current flows vertically.

[0005] More recently is also an attempt to implement a superconducting material of one or both of such vertical junction Josephson device of an oxide superconducting material such as _{YBa 2 Cu 3 O 6 ~ 8} .

[0006]

However, when a Josephson device is constructed by using an insulating film which is in close contact with the substrate surface, oxygen is not generated on the substrate surface or in the vicinity thereof as long as an oxide superconducting material is used. There was a tendency to run short of the amount that it should be. In some cases, even the superconducting property is lost on or near this surface. Therefore, it was found that the thickness of the portion that actually becomes the insulating layer becomes larger than the coherent length, and as a result, the tunnel current does not flow reliably. The present invention has been made to eliminate such drawbacks.

The present invention eliminates such drawbacks and provides a Josephson device having a lateral joint structure in which the upper surface is not used for the joint portion. In addition, the ultra-high frequency operation is provided in the four-terminal (three-terminal) circuit device, that is, the control electrode for applying the input signal and the electrode for deriving the output signal.

[0008]

In order to solve such a problem, the present invention has a non-superconducting property having a plurality of oxide superconducting materials and a structure similar to the oxide superconducting material, that is, a perovskite type structure. It is made of a material and has a structure in which a plurality of the oxide superconducting materials are connected to each other through the non-superconducting material. The material having non-superconducting properties is obtained, for example, by ion-implanting an additive into an oxide superconducting material. In the present invention, a substrate having a non-superconducting surface in which the same additive is added to the above-mentioned oxide superconducting material or a substrate in which the above-mentioned non-superconducting material is formed on a heterogeneous substrate may be used. A superconducting material having a single crystal or polycrystalline structure in which an ab plane (a plane perpendicular to the c-axis is referred to as a c plane or an ab plane) is oriented parallel to the upper surface of the substrate is used. In the present specification, the orientation that the ab plane is substantially parallel to the substrate (generally referred to as c-axis orientation) is due to the c-axis orientation in the X-ray diffraction pattern. It is meant that the relative intensities of the peaks are more than 10 times greater than that of the other ab axis orientations. Furthermore, isolation was performed by adding an additive that continues to lose superconducting properties when heat-treated also in the non-active regions around the periphery of the oxide superconducting material except the active region. This oxide superconducting material has a modified perovskite structure, and the current is c in the direction parallel to the ab plane.
It can flow 100 times more than in the axial direction. Therefore, making this direction parallel to the upper surface of the substrate can produce a large current density, which is effective for a fine process and high integration. By doing so, it is possible to further prevent oxygen from leaking upward at or near the upper surface of the modified perovskite structure in this structure. In addition, as described above, a protective film in which an additive that loses superconducting properties is added to the same material as the oxide superconducting material is provided on the upper surface or the upper part of the oxide superconducting material. Higher reliability can be obtained in all regions that should have superconducting properties by making the oxygen concentration of the same as or larger than that of the inside (bulk) of the oxide superconducting material.

The peripheral portion of the superconducting material thin film thus oriented is subjected to heat treatment to provide a non-active region to which an additive having non-superconducting properties is added, by an ion implantation method of the additive, etc. The active region to be constituted by the lead can be selectively provided without applying any photoetching to the unnecessary portion. If necessary, similar additives may be added to a part of the active region such as the Josephson junction surface (the central region or a region necessary for design).

The order of forming this step and forming the protective film on the upper surface may be reversed.

The present invention, as an example of a method for producing a non-superconducting oxide material having a finite resistance as described above, is added to a predetermined position in a zero resistance oxide superconducting material by an ion implantation method or the like. Was added and heat-treated to obtain an oxide material having finite resistance.

That is, iron (Fe), nickel (Ni), cobalt (Co), silicon (Si), germanium (Ge), boron (B) as additives added to the oxide superconducting material having superconducting properties. ), Aluminum (Al), gallium (Ga), phosphorus (P), titanium (Ti), tantalum (Ta), and magnesium (Mg). In such a case, the concentration of the additive is 1
It was set to -25 atom%. Among these, in particular, Mg and Al have the same valence as the oxide superconducting materials of Groups 2 and 3 of the periodic table of the elements, and are strongly bonded to oxygen by heat treatment to easily form an insulating material. Therefore, the additive is added to the oxide superconducting material 1 to
The superconducting property can be destroyed after the heat treatment by adding 10 atomic%, preferably 5 to 10 atomic%. And it has almost the same thermal expansion coefficient as this oxide material, and it is possible to prevent the occurrence of cracks due to temperature changes.

Further, elements constituting the oxide superconducting materials represented by 3a2a ₂ Cu ₃ O ₆ to ₈ , for example, Y of the 3a group element
(Yttrium), copper (Cu), 2a group element barium (Ba),
It may be an oxide non-superconducting material having the same main component as the oxide superconducting material containing calcium (Ca) more than necessary. In such a case, it is necessary to add it to such an extent that the stoichiometric ratio exhibiting superconductivity is disturbed. Specifically, 5 × 10 ²⁰ 〜 2.
The order is 5 × 10 ²² cm ^-3 . However, oxygen constituting a part of the oxide superconducting material is an unsuitable element because it is easily degassed to the outside in a subsequent thermal anneal in the implanted region.

The periodic table of elements in this specification is based on the dictionary of physics and chemistry (Iwanami Shoten, published April 1, 1963).

An example of the superconducting device of the present invention is shown in FIG.

In FIG. 2A, on the insulating substrate (1 ''),
A material that has non-superconducting properties and has the same main component as the superconducting material (1 ')
The substrate (1) having and was used. A thin film (30) of an oxide superconducting material was formed on the entire surface. Then, the oxide superconducting materials (3) and (9) are left in order to isolate the surrounding area to make it an inactive region, and the surrounding area is subjected to an accelerating voltage of 300 to 2000 KeV and Al, Mg And other additives are ionized and injected. By this ion implantation method, the superconducting material is added across (both above and below and in the anterior-posterior direction of the drawing) to form the inactive region (20). At the same time, the thickness of the first oxide material (4) for the device in the active region (2) (left and right direction of (4) in Fig. 2 (A)) is made as thin as possible, preferably 1000 Å or less. It was made to have a Son junction effect or a proximity effect.

This area (4) is 1/2 to 1/10 that of the peripheral area.
The concentration was doubled (0.1 to 20 atom%). For the periphery (20)
Al and Mg were added at a concentration of 5 to 10 atom%.

Further, an oxide superconducting thin film (40) is formed on the entire surface by the same method, the active regions are covered with the non-active regions (11), and the connecting portions (8 ') P (for electrode) are formed. Only 9 ') and the active region selectively retain the superconducting property. Then, in the same manner, a third oxide superconducting thin film (50) is formed on this. Then, except for the regions of the leads (8) and (9), the same additives as described above are added to the unnecessary thin film in the other regions (21) for insulation. Then, the pair of electrode / leads (8) and (9) for output is formed into a multi-layer wiring, and all active regions of the device, the electrodes, the electrode connecting portions, and the leads are formed of an oxide superconducting material. Further, the non-active region in the peripheral portion can be insulated by adding an additive capable of imparting non-superconducting properties thereto by heat treatment.
Since the electrodes (9), (9 ') and (5) are both oxide superconducting materials and their orientation is such that the ab plane is parallel to the substrate, there is no problem.

Thus, the Josephson device (2) was constructed to obtain the characteristics shown in FIG.

In addition to such a two-terminal device, the present invention also provides a sufficiently large electrical resistance, preferably a first superconducting material, between electrodes connected between a pair of output oxide superconducting materials. A coating having an electric resistance 10 times or more higher than the electric resistance may be provided on the upper surface, the lower surface or both surfaces thereof, and the control electrode may be provided in close contact therewith. Two such examples are shown in FIGS. 2 (B) and (C).
Shown in

In FIG. 2 (B), the control electrode (10) is provided above the first oxide superconducting material (30), and the electrode and the multilayer wiring connecting portions (8 '), (9') are provided. ) And electrodes / leads (8), (9), (10)
Both are made of oxide superconducting material.

In FIG. 2C, the control electrodes (10) and (10 ') of the oxide superconducting material are provided on both upper and lower surfaces of the region (4).

The interlayer insulators (11) and (11 '') also have the same coefficient of thermal expansion or the same main component as the isolation region, with the addition of 1 to 30 atomic% of additive, typically 5 to 10 atomic%. It is good to

In FIGS. 2 (B) and 2 (C) of the present invention, a film having an electric resistance sufficiently larger than the electric resistance of the oxide superconducting material, preferably, between the control electrode and the superconducting film. The insulating film (11) was provided only above the oxide superconducting material (30) thereunder by adding the above-mentioned additive. Then, a voltage is applied from the control electrode (10) made of an oxide superconducting material which is an input terminal, and a voltage is applied to the first oxide material (4) below the control electrode. This material is in an intermediate state between a state with complete superconductivity and a state without superconductivity at all (partly superconducting and partly non-superconducting state, that is, Tc onset and Tco (State of temperature region between and) Further, since it has semiconductor or insulator characteristics, it is possible to change and control its own potential according to the voltage applied to the input control electrode.

In FIG. 2 of the present invention, the second oxide superconducting materials (3) and (5) are formed on the entire surface, and a large amount of the additive used in the present invention is added to the outer periphery of a desired shape. Measure the insulation separation (20) from the adjacent device. Therefore, after adding the additives as described above, or if each of these steps is performed a plurality of times, or after each of these steps, the whole of these is 400 to 1000 in oxygen.
C., 0.5 to 50 hours, for example, 900.degree. C. for 3 hours and gradually cooling to 400.degree. C. and annealing at oxygen at this temperature for 1 hour to remove impurities from the oxide or oxide superconducting material. The parts were replaced and the crystal structure was arranged.

According to the present invention, the oxide superconducting material is not formed only in the first layer on the same substrate, but is laminated on the second layer to form the oxide superconducting material.
A layer or even a third layer of oxide superconducting material can be made. The active region is selectively formed with respect to these by forming an inactive region by adding an additive. Contrary to that shown in FIG. 2, the first layer may be an electrode / lead and the second layer may be a device. It is also possible in the present invention to arrange the device for each layer. The substrate (1 ″) in FIG. 2 may be a silicon substrate provided with a semiconductor integrated circuit. Then, the silicon integrated circuit and the superconducting device can be integrated. At that time, since the difference in the coefficient of thermal expansion is removed, the buffer layer of (1 ′) of FIG. 2 is particularly effective.

[0027]

With such a structure, it becomes possible to manufacture a lateral junction type highly reliable electronic device using a superconducting material.

Since the oxide superconducting material has the ab plane aligned parallel to the plane of the substrate, its upper surface is also flat, and the peripheral portion is also insulated by adding an additive thereto, and the multi-layer wiring is also disconnected. It was possible to eliminate the hindrance to the characteristics.

Thus, a plurality of devices can be made, and when the devices are connected based on the design logic to make a superconducting integrated circuit, their interconnections can be made with zero resistance.

Embodiments will be described below with reference to the drawings.

[0031]

EXAMPLE Example 1 This example shows the structure of FIG. 2 (A).

YSZ (Ytterb Stabilized Zircon) was used as the substrate (1 ″). A non-oxide superconducting material (1 ') is formed on top of this by using a magnetic field application plasma coating method, MBE (Molecular Beam Epitaxial) method, CVD (vapor phase reaction) method, sputtering method, etc. , Substrate (1)
And Furthermore, an oxide superconducting material (30) was formed on this by the same method without adding an additive. Part 1
As an example, (A _1-x Bx) yCuzOw, x = 0.1 to 1, y = 2.0 to 4.
0 preferably 2.5-3.5, z = 1-4, preferably 1.5-3.
5, W = 4-10, preferably 6-8. A is Y (yttrium), Gd (gadolinium), Yb (ytterbium), Eu (
Europium), Tb (terbium), Dy (dysprosium),
Ho (holmium), Er (erbium), Tm (thulium), Lu (
Lutetium), Sc (scandium) or other elements are selected from one or more of Group 3a of the Periodic Table.

B is Ba (barium), Sr (strontium),
1 selected from 2a group of the periodic table of Ca (calcium)
Use one or more elements. Especially as a concrete example
Using _{(YBa 2) Cu 3 O 6} ~ 8. Further, as A, a lanthanide element or actinide element other than the above-mentioned elements in the periodic table can be used.

Simultaneously with or after this formation, 600-9
It was prepared by treating the hot anneal at a temperature of 50 ° C. for 5 to 20 hours and then gradually cooling. Thus, the oxide superconducting material (30) had a Tco of 91K as a characteristic of the superconducting material provided underneath with the oxide superconducting material (1 ') of the same main component. .

Next, an impurity such as magnesium or aluminum is added to the periphery (20) of the region where the device is to be formed by an ion implantation method for insulation. Further, the impurity is added to the region (4) by reducing it by about 1/5. That is, in FIG. 2A, a photoresist is provided on the regions (3) and (5), and the regions (4) and (20) without the resist are formed.
Only, selectively, the additive was added by the ion implantation method. The inactive region (20) was provided by adding an additive of aluminum or magnesium to a concentration of 5 to 10 atomic%, for example, 8 atomic%. After that, the photoresist was removed, and a thin film (40) of a second layer oxide superconducting material was formed again on the entire surface. Then, the other parts except the connecting parts (8 ') and (9') were made into the inactive region by the ion implantation method. Thus, a passivation film could be formed above the active region 12 by using the same main component material to which the additive was added. This was repeated once again to prepare the oxide superconducting material (50) for the second layer, and the leads (8) and (9) and the inactive region (21) were provided using the material. After this, all of these are placed in an oxidizing atmosphere for about 300 to 9
The entire surface is oxidized at a temperature of 50 ° C, for example 900 ° C, and each film is fitted together, and after stacking them to 400 ° C, oxygen is reduced from the stoichiometric ratio by the oxidation process by the ion implantation method again. If necessary, it was added to the interfacial region that had been removed. The heat treatment described above oxidizes the previously added additive and transforms this region into an insulator. Thus, the characteristics of FIG. 3 could be created in the structure of FIG. 2 (A).

Example 2 Further, FIG. 2B was manufactured by the same method. In this structure, a silicon substrate was used as the substrate (1 ″), and an integrated circuit was already made. Then, a silicon oxide or silicon nitride insulating film is provided thereon. In order to match this with the coefficient of thermal expansion, the oxide non-superconducting material (1 ') is used as shown in Fig. 2 (B).
The substrate (1) was provided with a thickness of μ. Furthermore, the active region (2) and the non-active region (2
0), an upper oxide superconducting material (1 ') was made. Especially the Lee
When forming the electrodes (8) and (9), the control electrode (10) was also formed by adding the additive to the peripheral portion at the same time. The output electrode was in close contact with the ceramic thin film so that an ohmic contact could be made. When the electrical characteristics of such a device were examined, the results shown in FIG.
It was found that it has the Josephson characteristic shown in Figure 3 at liquid nitrogen temperature.

Communication line with semiconductor integrated circuit (1 '') is 400 ° C
The above heat treatment was not performed, and the oxide superconducting material was formed at a temperature up to 400 ° C. This is to prevent oxygen of the oxide superconducting material and silicon constituting the semiconductor from reacting with each other to form silicon oxide at the interface.
If it is unavoidable to raise the temperature above this, the interface should be silicon-heat-resistant metal (W, Mo, Ti or its silicide)-
Non-oxidizing metal (Au, Ag) -oxide superconducting material, 700
It can withstand processing or film formation for up to 1 hour at ℃.

[0038]

According to the present invention, the superconducting device, which has been a vertical-junction type two-terminal device up to now, is changed to a lateral-junction type two-terminal device or a multi-terminal device, which are integrated on the same substrate.

Further, since the electrode / lead is composed of a two-layer wiring, the wiring is made of an oxide superconducting material having a resistance of zero or sufficiently close to zero in such a temperature range.

Therefore, it becomes possible to provide a large number of superconducting devices on the same substrate and integrate them.

In the present invention, 0 or 1 control electrode is shown, but 2 or more control electrodes may be provided in series or in parallel.

At the same time, the periphery of the substrate was selectively separated with an insulator. You may make a superconducting coil and use it as a SQUID.

In the present invention, the title oxide superconducting material was used. However, this is because the superconducting material is an oxide. It is clear from the technical idea of the present invention that the crystal structure may be polycrystalline or single crystal. Particularly in the case of a single crystal structure, when using a superconducting material, epitaxial growth may be performed on the substrate.

Further, in the embodiments of the present specification, an example in which a material which is made non-superconducting by ion-implanting the superconducting material is used for connection between the superconducting materials is shown. However, it goes without saying that it can be obtained by another method, for example, by patterning a superconducting thin film with a laser and depositing a non-superconducting material having a perovskite type structure thereon.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a conventional superconducting device.

FIG. 2 is a vertical sectional view of a superconducting device of the present invention.

FIG. 3 Characteristics of superconducting device made according to the present invention

Claims (1)

[Claims] 1. A plurality of oxide superconductors provided on a substrate.
The material has the same main component as the oxide superconducting material and has a non-superconducting property.
An oxide superconducting device comprising a conductive material , wherein the plurality of oxide superconducting materials have an ab plane on a substrate.
A material that is oriented so as to be substantially parallel and that has the non-superconducting properties of the oxide superconducting material.
And are laterally joined to the oxide superconducting device.
Place.